Update ping-input-plugin Readme (#2651)

plugins/inputs/ping/README.md

-# Ping input plugin
+# Ping Input plugin
 
 This input plugin will measures the round-trip
 
-## Windows:
 ### Configuration:
+
 ```
-	## urls to ping
-	urls = ["www.google.com"] # required
-	
-	## number of pings to send per collection (ping -n <COUNT>)
-	count = 4 # required
-	
-	## Ping timeout, in seconds. 0 means default timeout (ping -w <TIMEOUT>)
-	Timeout = 0
+# NOTE: this plugin forks the ping command. You may need to set capabilities
+# via setcap cap_net_raw+p /bin/ping
+[[inputs.ping]]
+## List of urls to ping
+urls = ["www.google.com"] # required
+## number of pings to send per collection (ping -c <COUNT>)
+# count = 1
+## interval, in s, at which to ping. 0 == default (ping -i <PING_INTERVAL>)
+# ping_interval = 1.0
+## per-ping timeout, in s. 0 == no timeout (ping -W <TIMEOUT>)
+# timeout = 1.0
+## interface to send ping from (ping -I <INTERFACE>)
+# interface = ""
 ```
+
 ### Measurements & Fields:
+
 - packets_transmitted ( from ping output )
 - reply_received ( increasing only on valid metric from echo replay, eg. 'Destination net unreachable' reply will increment packets_received but not reply_received )
 - packets_received ( from ping output )
@@ -25,12 +32,16 @@ This input plugin will measures the round-trip
     - average_response_ms ( compute from minimum_response_ms and maximum_response_ms )
     - minimum_response_ms ( from ping output )
     - maximum_response_ms ( from ping output )
-	
+
 ### Tags:
-- server
+
+- host
+- url
 
 ### Example Output:
+
 ```
+$ ./telegraf -config telegraf.conf -input-filter ping -test
 * Plugin: ping, Collection 1
 ping,host=WIN-PBAPLP511R7,url=www.google.com average_response_ms=7i,maximum_response_ms=9i,minimum_response_ms=7i,packets_received=4i,packets_transmitted=4i,percent_packet_loss=0,percent_reply_loss=0,reply_received=4i 1469879119000000000
 ```

plugins/inputs/ping/ping.go

@@ -49,7 +49,7 @@ const sampleConfig = `
   ## NOTE: this plugin forks the ping command. You may need to set capabilities
   ## via setcap cap_net_raw+p /bin/ping
   #
-  ## urls to ping
+  ## List of urls to ping
   urls = ["www.google.com"] # required
   ## number of pings to send per collection (ping -c <COUNT>)
   # count = 1